We conduct a two-stage (DEA and regression) analysis of the efficiency of New Zealand secondary schools. Unlike previous applications of two-stage semi-parametric modelling of the school “production process”, we use Simar and Wilson’s double bootstrap procedure, which permits valid inference in the presence of unknown serial correlation in the efficiency scores. We are therefore able to draw robust conclusions about a system that has undergone extensive reforms with respect to ideas high on the educational agenda such as decentralised school management and parental choice. Most importantly, we find that school type affects school efficiency and so too does teacher quality.